It has previously been proposed to construct centrifuges in such a manner that a flexible bag is supported in a rotor which is connected to one, or more flexible conduits which, during operation, flex in re-entrant loops or bights, thereby eliminating rotary joints and the like. In one such construction, described and proposed in detail in patent application Ser. No. 930 389, filed Aug. 2, 1978, Westberg, entitled "Apparatus for Accomplishing Unlimited Relative Rotation of the Ends of a Filiform Transmission Element", and corresponding to German Published Patent Disclosure Document No. OS 23 54 368, a plurality of coaxial, nested rotors are independently driven. The rotor structure of the present invention is an improvement over that described in the aforementioned application. Other rotary structures which permit connection to filiform elements, without rotary joints, are described in the referenced patents.
The centrifuge has three independent rotors, nested within each other, the innermost rotor supporting and retaining the separating container in which the liquid, typically blood, is to be placed and, from where, upon separation, the separated components drawn off. The axes of rotation of the respective rotors are all aligned in a straight line along the common central axis of the rotors. The outermost rotor is driven by a motor, for example by a belt drive; the intermediate rotor is connected by a slipfree connection with the outer rotor to be driven therefrom in a direction of rotation opposite to that of the outer rotor. The inner rotor is driven by means of a flexible, torque-transmitting element, such as a spiral spring, or an elongated spiral arrangement. The elongated spiral also receives a multiple channel or duct tubular element of flexible plastic, which forms the connection to the separating container. Upon rotation of the outer rotor, driven by the motor, the intermediate rotor will rotate in an opposite direction, for example with the same speed. The inner rotor is driven at a speed which is a multiple, typically the four-fold mutliple of the other two rotors, driven by the spiral. This arrangement, described, for example, in the aformentioned patent application and published German Patent Disclosure Document No. DE-OS 23 54 368, has the advantage that rotary joints or couplings which are both liquid-tight while permitting relative rotation can be avoided.
It has been found that different torsional relationships of the spiral, friction, and preferential direction of bending will result in rotation of the inner rotor at speeds which vary and are not always constant; rather, the rotary speed of the inner rotor changes in accordance with instantaneously existing frictional conditions, bending conditions of the spiral, or the like, resulting in a superimposed change or modulation of the average speed of the rotor, that is, either leading or trailing of the inner rotor with respect to an average position which would be determined by an average speed. Transmission of torque by means of a spiral, particularly a flexible spiral spring, is limited. Thus, the starting time and braking time have to be comparatively long in order to permit transmission of sufficient torque from the outer rotor to the innermost rotor for acceleration thereof.